1. Field of the Invention
The present invention relates to an image capturing device, a color measuring device, a color measuring system, and an image forming apparatus.
2. Description of the Related Art
In image forming apparatuses, such as printers, processing called color management is performed in order to enhance reproducibility of an output relative to an input by reducing fluctuations in the output caused by characteristics unique to each individual device. The color management may, for example, be performed by the following techniques. Specifically, an image of a color chart of a reference color (patch) is actually output using the image forming apparatus (the patch output as an image by the image forming apparatus will hereinafter be referred to as a “color measurement target patch”) and the color measurement target patch is then subjected to color measurement using a color measuring device. A color conversion parameter is then generated based on a difference between a calorimetric value obtained from the color measurement target patch and a color specification value of the reference color corresponding thereto in a standard color space. The color conversion parameter is then set in the image forming apparatus. When thereafter outputting an image according to image data input thereto, the image forming apparatus subjects the input image data to color conversion based on the set color conversion parameter and outputs an image based on image data after the color conversion. The image forming apparatus can thereby output an image with high reproducibility and with reduced fluctuations in the output caused by characteristics unique to each individual device.
In such color management, spectrophotometers are widely used as the color measuring device performing color measurement of the color measurement target patch. The spectrophotometer provides a spectral reflection factor for each wavelength and is thus capable of performing color measurement with high accuracy. The spectrophotometer is, however, an expensive instrument having a large number of sensors mounted therein and a need thus exists for color measurement with high accuracy using a lower cost instrument.
Exemplary methods for achieving color measurement at low cost include use of an image capturing device that includes an image sensor, the image capturing device capturing an image the color measurement target as a subject and an RGB value of the subject obtained by the image capturing being converted to a color specification value in the standard color space. For example, Japanese Patent No. 3129502 discloses a technique in which a reference color chart is placed near a subject that serves as the color measurement target, a reference color chart serving for comparison with the subject, the subject and the reference color chart are simultaneously imaged with a color video camera, and RGB data of the reference color chart to be obtained through the image capturing is used to correct RGB data of the subject before the RGB data of the subject being converted to a color specification value in the standard color space.
With the technique disclosed in Japanese patent No. 3129502, however, it is difficult to maintain a positional relation among the subject, a light source, and the color video camera, which results in image capturing conditions being varied, so that image capturing cannot be performed stably.
Therefore, there is a need for an image capturing device, a color measuring device, a color measuring system, and an image forming apparatus capable of performing stable image capturing.